1. Field of the Invention
The present invention relates to a high-frequency discharge ignition coil apparatus and a high-frequency discharge ignition apparatus, mainly used for driving an internal-combustion engine.
2. Description of the Background Art
In recent years, problems such as environmental conservation and fuel depletion have arisen, and there is an urgent need to address such problems in automobile industry.
As an example of efforts to address such problems, there is a method of dramatically improving fuel consumption by engine downsizing and weight reduction using a supercharger.
It is known that in a highly supercharged state, the pressure in an engine combustion chamber becomes extremely high even when combustion is not occurring, and in this situation, it is difficult to cause spark discharge for starting combustion.
One of the reasons for the difficulty is that required voltage for causing insulation breakdown between (in the gap) a high-voltage electrode of an ignition plug and a GND (ground) electrode becomes extremely high, and then exceeds the withstand voltage of an insulator portion of the ignition plug.
In order to solve the above problem, study for increasing the withstand voltage of the insulator portion has been conducted. However, in actual, it is difficult to ensure sufficient withstand voltage for the requirement, and there is no choice but to employ means of narrowing the gap interval of the ignition plug.
However, if the gap of the ignition plug is narrowed, then the influence of the quenching operation by the electrode portion becomes large, so that problems such as reduction in starting performance and reduction in combustion performance arise.
In order to solve the above problems, avoidance means of giving, by spark discharge, energy exceeding heat taken by the quenching operation of the electrode portion, or causing combustion at a position as far possible from the electrode, is conceivable. For example, an ignition coil apparatus as shown in Patent Document 1 is proposed.
In the ignition coil apparatus disclosed in Patent Document 1 (Japanese Laid-Open Patent Publication No. 2012-112310), while spark discharge is caused in the gap of the ignition plug by using a conventional ignition coil, high-frequency current is applied to a path of the spark discharge via a mixer using a capacitor, thus making it possible to cause spark discharge with high energy and form discharge plasma spreading more widely than normal spark discharge.
The conventional ignition coil apparatus shown in Patent Document 1 separates or couples a high-voltage system and a large current system by using a high withstand voltage capacitor.
Generally, a capacitor has a temperature characteristic, and its capacitance varies in accordance with variation in the environmental temperature.
The conventional ignition coil apparatus shown in Patent Document 1 has a problem that, since AC current corresponding to the pass frequency band of the capacitor is applied to the path of spark discharge, if the characteristic of the capacitor varies by the temperature, the level of current applied to the path of spark discharge greatly varies, so that current cannot be applied stably.